A new study says groundwater depletion releases a significant amount of carbon dioxide into the atmosphere that has until now been overlooked by scientists in calculating carbon sources.

The study’s authors estimate groundwater depletion in the United States could be responsible for releasing 3.8 billion pounds of carbon dioxide to the atmosphere every year.

Based on these figures, groundwater depletion should rank among the top 20 sources of carbon emissions documented by the U.S. Environmental Protection Agency and the Intergovernmental Panel on Climate Change. This would mean the carbon dioxide emitted through groundwater depletion is comparable to the carbon generated from aluminum, glass, and zinc production in the United States, according to the study’s authors.

Groundwater depletion’s impact on carbon emissions is significant yet relatively small compared to the leading contributors, according to the authors. For example, scientists estimate fossil fuel combustion in the United States is responsible for releasing more than 5 billion metric tons (11 trillion pounds) of carbon dioxide into the atmosphere every year, close to 3000 times the amount released from groundwater depletion.

Still, the study’s authors argue that understanding all sources of carbon dioxide emissions is important for making accurate climate change projections and finding solutions.

“It’s not going to change the way we think about global climate change. It’s just another factor involved that we need to consider,” said Warren Wood, Ph.D., a hydrogeologist at Michigan State University and co-author of the new study. Wood served as editor of NGWA’s Groundwater® from 1996-2001, the 2002 NGWA M. King Hubbert Award recipient, and 1997 NGWA Life Member Award winner.